PROJECT SUMMARY. The QUIT-Mobile study proposes to use mobile phone self-monitoring and feedback to enhance and sustain over 12-months the impacts of the Quit Using Drugs Intervention Trial (QUIT), an ef- fective screening and brief intervention (SBI) previously successful in reducing risky drug use (i.e., moderate use) in low-income, diverse patients over a 3-month follow up. We propose to conduct the QUIT-Mobile study for primary care patients who receive care in 8 clinics of federally qualified health centers (FQHC) in Southern California over 12-months follow up, comparing to QUIT and Usual Care (UC). The proposed study is an Effec- tiveness-Implementation Hybrid Type 1 design consisting of a single-blind, 3-arm, RCT with adult, mostly La- tino FQHC primary care patients with risky drug use (ASSIST score 4-26), randomized to 3 conditions (n=320/arm, n=960 total): 1) QUIT-Mobile; 2) standard QUIT; 3) Usual Care. Qualitative data on implementa- tion facilitators and barriers will inform future scale-up and sustainability, in addition to cost data and cost-effec- tiveness analysis. The aims are to examine effectiveness in reducing risky drug use and cost-effectiveness comparing the three arms over 3-, 6- and 12-months. Drug use measures include urine drug tests, and timeline follow-back self-reports for past 7-days and past 30-days (risky drug users have sporadic drug use patterns requiring longer self-report recalls for drug use that urine screens may not detect). The 3-arm study enables testing of the independent and synergistic effects of QUIT-Mobile compared to QUIT and both to Usual Care, acknowledging that mHealth components alone may not be effective outside of a clinical/coaching relationship. The 12-month timeline reflects anticipated scale-up scenarios of annual primary care visits when screening and brief intervention would be repeated routinely. QUIT contains 3 components: 1) patient screening with the WHO ASSIST, 2) brief clinician advice (<4 minutes) including opioid overdose prevention education, and 3) 2- and 6-week telephone drug-use health coaching sessions utilizing motivational interviewing and cognitive be- havioral techniques, delivered by paraprofessional health coaches. QUIT-Mobile proposes to test the addition of mobile phone self-monitoring, feedback, and coach monitoring dashboard to enhance and sustain QUIT's drug use reductions using mobile app, text-messaging (SMS), or interactive voice response (IVR) to allow par- ticipation by with varying technological preferences. This study does not test which technology platform is more effective, but rather, the effectiveness of the intervention functions (i.e., self-monitoring, automated feedback, coach monitoring) that are delivered via patients' preferred technologies. This study is novel and timely in inte- grating massively scalable mobile phone tools into an effective primary care BI to prevent substance use disor- der (SUD) in FQHC patients delivered by paraprofessionals. QUIT-Mobile is responsive to the National Opioid Crisis, and the US Mental Health Parity Act and National Academy of Medicine recommendations to integrate behavioral health SBIs into primary care settings to prevent higher level SUD requiring specialty treatment.